The Structure of DNA - The Double Helix

What does it look like

a twisted ladder

what is it made of

Long chains of individual units called NUCLEOTIDES

Each nucleotide is composed of what

5 CARBON SUGAR (deoxyribose) and a PHOSPHATE GROUP (together they are the backbone) and one of the five NITROGEN-CONTAINING BASES (the rungs of the ladder)

Nitrogen bases from one strand of DNA connects to a what

COMPLEMENTARY NITROGEN BASE on the other strand of DNA by HYDROGEN BONDS

(A-T = 2 hydrogen bonds)

(G-C = 3 hydrogen bonds)

The 4 NITROGENOUS BASES found in DNA are

• Adenine (A)

• THYMINE (T)

• Guanine (G)

• CYTOSINE (C)

RNA contains what instead of what

Contains URACIL (U) instead of THYMINE (T)

Bases are divided into two types

PURINES - double ring structure (A and G)

PYRIMIDINE - Single ring structure (T, C and U)

Chargaff’s rule states what

ADENINE ONLY bonds with THYMINE and GUANINE with CYTOSINE

The strands are put together how

ANTI-PARALLEL so that one strand is “upside-down) compared to the other

It is estimated the human genome contains about how many base pairs of DNA in how many chromosomes

3 billion base pairs of DNA in 46 chromosomes

Uncoiled each chromosomes averages about how long

5cm in length